drm/i915/dp: try to read receiver capabilities 3 times when detecting

If ->detect is called too soon after a hot plug event, the sink may not
be ready yet.  So try up to 3 times with 1ms sleeps in between tries to
get the data (spec dictates that receivers must be ready to respond within
1ms and that sources should try 3 times).

See section 9.1 of the 1.1a DisplayPort spec.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index a9a5051419df..70075d9900da 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1551,6 +1551,7 @@ static enum drm_connector_status
 ironlake_dp_detect(struct intel_dp *intel_dp)
 {
         enum drm_connector_status status;
+        int ret, i;
 
         /* Can't disconnect eDP, but you can close the lid... */
         if (is_edp(intel_dp)) {
@@ -1561,12 +1562,16 @@ ironlake_dp_detect(struct intel_dp *intel_dp)
         }
 
         status = connector_status_disconnected;
-        if (intel_dp_aux_native_read(intel_dp,
-                                     0x000, intel_dp->dpcd,
-                                     sizeof (intel_dp->dpcd))
-            == sizeof(intel_dp->dpcd)) {
-                if (intel_dp->dpcd[DP_DPCD_REV] != 0)
+        for (i = 0; i < 3; i++) {
+                ret = intel_dp_aux_native_read(intel_dp,
+                                               0x000, intel_dp->dpcd,
+                                               sizeof (intel_dp->dpcd));
+                if (ret == sizeof(intel_dp->dpcd) &&
+                    intel_dp->dpcd[DP_DPCD_REV] != 0) {
                         status = connector_status_connected;
+                        break;
+                }
+                msleep(1);
         }
         DRM_DEBUG_KMS("DPCD: %hx%hx%hx%hx\n", intel_dp->dpcd[0],
                       intel_dp->dpcd[1], intel_dp->dpcd[2], intel_dp->dpcd[3]);